The present invention pertains to the field of acoustic cardiography, and more specifically focuses, within this field, on methodology for controlling cardio-assisted, pacemaker (implanted or external) pacing characteristics in relation to a pacemaker-equipped subject who is potentially at risk for ischemia and sudden, cardiac death—the former being potentially a key factor leading and contributing to the latter. The methodology is based on using, as pacemaker therapy-control values, what are referred to herein as acoustic cardiographic therapy (AC) values, which are calculated from certain, selected, acquired ECG-and-heart-sound-associated parameters. Those skilled in the art will recognize that this acoustic-cardiography field involves, as was just suggested, the cooperative, information-integration use of both ECG and heart-sound information—information which is processed in different ways to obtain, selectively, various important heart-functionality parameters that especially correlate to, and help one to understand, the behavior of a subject's heart which is relevant to the matters of status of potential, impending or present ischemia and the risk of sudden cardiac death. Such integration characterizes and underpins important aspects of the present invention which offers a unique approach for addressing these two, serious heart-disease, heart-failure issues. Heart-functionality parameters which are key factors in the practice of this invention are LDPT (S2-Q), % LVST, S3 strength, S4 strength, and % EMAT, with particular emphasis resting on LDPT (S2-Q) and % LVST each of which is based upon combined ECG and heart-sound information.
In connection with practice of the present invention, I have discovered that, among all five of the just-mentioned, important, heart-functionality parameters, LDPT and % LVST, employed differently (individually for LDPT, and combinedly with each other or with others of the five parameters, as will be explained below) in the calculation of AC values, offer a very high likelihood of predicting both the potential onset and or presence of ischemia, as well as the onset of sudden cardiac death.
In this regard, and considering a principal focus of the present invention, the mechanism(s) involved with ischemia and sudden cardiac death may be thought of in the following fashion. In connection with this discussion, one may wish to make reference to FIG. 3 in the drawings which illustrates progressive, time-based changes in heart functionality (pictured in relation to the two most significant heart-functionality parameters, LDPT and % LVST) leading, via dangerous changes occurring in ischemia, to sudden cardiac death. Once the heart becomes more ischemic, it stiffens, and it takes longer to fill during cardiac cycles. At the same time, ischemia can seriously damage the heart so much that the heart's pumping function also becomes impaired, and since the heart is required to maintain a subject's blood pressure, it has to pump longer and with greater difficulty to deal with a resulting, further impaired filling function. Since cardiac perfusion happens during diastolic filling, and mainly during the important S2-Q interval (LDPT), a serious, associated consequence is that the heart receives less of an oxygen supply under such circumstances. Under stress, this perfusion time can become impaired so much that even more heart muscle dies, and the overall victim ventricle becomes more vulnerable for lethal tachyarrhythmia—the key, and highly dangerous, event which results in so-called sudden cardiac death.
As will become apparent, practice of the present invention can provide effective early warnings which can preemptively counteract, or at least significantly impair and minimize, these two, related, dangerous heart conditions.
In connection with the importance, in practicing the instant invention, of using heart-sound information along with ECG information, the utility of ECG information in relation to detecting various heart-failure issues, such as those which concern the present invention, or to help significantly with the management of heart-failure patients, is extremely limited, since the relevant electrical information does not contain any mechanical information reflective of the heart's pumping function and filling dynamics. Accordingly, complementing ECG information with heart-sound information for monitoring heart-failure patients improves the utility of any methodology, and of any device, such as a Holter device, in terms of addressing the ischemia and sudden cardiac death risk categories of problems associated with heart disease.
For example, while ECG information, in particular when recorded during exercise stress, has clear utility in the detection and management of ischemic heart diseases, the relevant ECG parameters, like the ST segment depression, are not sensitive enough to enable ECG testing to stand alone as a test with respect to the diagnosis of the disease characteristics which are the concern of the present invention. As an illustration, a proper diagnosis of ischemia typically requires the utilization of several other kinds of tests, such as blood tests, stress echo tests, etc., in order to yield something approaching conclusive evidence of a potential or actual ischemia condition. Further, the utility of ECG information to detect ischemia is significantly reduced in relation to implanted monitors, due to the limited number of available ECG vectors, and the location of the relevant ECG leads. Additionally, for the electrical markers of ischemia to be specific, a significant amount of heart tissue has to have been previously compromised through the lack of oxygen supply, and thus, such markers often produce information which is actually—reflective of an in-place, aggressive and irreversible ischemia condition.
Heart sounds can complement the electrical markers made available by ECG information relating to ischemia in two different ways. One of these ways involves examining changes that take place in fluid dynamics during the filling phases of the ventricles to reveal an abnormally short, and therefore impaired, blood supply condition for the heart, before heart tissue is damaged and the relevant electrical markers become elevated in strength. In this context, principal cardio-functionality parameters which are very relevant include LDPT (S2-Q), % LVST, S3 strength, S4 strength, and EMAT, with, as mentioned above, key emphasis resting principally on LDPT (S2-Q) and % LVST—both directly involving combined ECG and heart-sound information. The second way involves a situation respecting conditions wherein (a) ECG electrical markers are confounded through the lack of a sufficient number of ECG leads, or because of poor ECG information quality, as well as in (b) situations where temporary tissue damage is not sufficient to elevate the relevant electrical ECG markers. Heart sounds will, in these circumstances, reflect the change in diastolic or even systolic function due to ischemia, and therefore will indicate the impact of the ischemic parts of the heart relative to the pumping and filling functions of the heart.
In this setting, while it will be very evident to those skilled in the art that the methodology of the present invention may be employed successfully in a number of different heart-failure, heart-pacing environments, a preferred and best-mode approach toward practicing the invention is disclosed herein, for illustration purposes, specifically in the context of biventricular, pacemaker pacing associated with the use of an otherwise conventional, portable/ambulatory, Holter monitoring and recording device—a context wherein the invention has been found to offer particular utility.
As will be seen from the detailed description of the invention which is presented below, the methodology of the invention is especially focused on addressing ischemia and sudden cardiac death risk issues involving an ambulatory, heart-failure patient who is equipped with either an internal or an external pacemaker, such as a biventricular pacemaker, along with a classic Holter device which is capable of (a) processing input information relating to pacemaker and heart activities, (b) storing relevant information, and (c), when associated with an appropriately algorithmically programmed digital computer (internal or external), responding to real-time, monitored heart behavior to perform controls and adjustments in the operation of the associated pacemaker.
More specifically, and as will be seen, implementation of the present invention focuses, on the development and defining (computer calculation) of what is referred to herein as an acoustic cardiographic therapy, or control, (AC) value (also referred to simply as an AC Value). This AC Value “entity”, utilizing computer processing, is determined from (i.e., is based upon) one or more heart-functionality parameter(s) that are especially relevant to the ischemia and risk of sudden cardiac death issues. In this setting, the invention specifically recognizes the special utility, in different circumstances, of several, important heart-functionality parameters as bases for calculating, and then employing, AC Values that are deemed to be the most useful for controlling the pacing operation of a pacemaker, such as pacing rate, pacing strength and atrioventricular (AV) and interventricular (IV) delay times. These parameters are five in number. As mentioned earlier, they include LDPT (S2-Q), % LVST, S3 strength, S4 strength, and EMAT.
In certain circumstances, the LDPT (S2-Q) parameter may be used as an averaged singularity for AC-Value calculation purposes, or may be used in an averaged and mathematically combined condition along with % LVST. In certain other circumstances, an appropriate averaged and computed mathematical combination of the five parameters may be the best to use, always including at least one of LDPT (S2-Q) and % LVST. Other averaged, combinational choices are certainly possible, and those skilled in the relevant medical arts will understand how to choose AC-Value-basing parameters from the detailed description of the invention which is presented below. Non-exclusive illustrations of averaging and mathematical combining of heart-functionality parameter values involved in the calculation of AC values are given below.